The movement and handling of freight, for example in the form of containers, often involves the use of a conveyor track on which the freight article is movably supported. The conveyor track may include caster roller units each comprising at least one support roller which is mounted on a roller carrier rotatably about its axis of symmetry. The roller carrier is mounted on a base rotatably about an axis which is arranged eccentrically and perpendicularly with respect to the axis of rotation of the support roller.
Caster roller units of that kind, as can be found for example in U.S. Pat. specification No. 3,435,938, are used whenever an article is to be moved over a normally horizontal floor surface on which it is supported, and in that situation is to be provided with a `weak` guiding action in its respective direction of movement. In that connection the term `weak` guiding action means that the article to be moved is subjected to a stronger guiding action than is the case for example when it rests on ball-type support array, but on the other hand the guiding action is not so rigid that the direction of movement of the article cannot be altered at any time. When such an alteration in the direction of movement has occurred, then the same `weak` guiding action is to take effect in the new direction of movement, as in the preceding direction of movement.
Such a caster roller unit generally comprises two support rollers which are mounted on a roller carrier in juxtaposed relationship in such a way that their axes of symmetry about which they are rotatable independently of each other are in alignment with each other. The unit may be mounted either on a surface over which the article to be moved is actually moved, as in the case of a conveyor track as mentioned above, but equally it may be mounted on the actual article to be moved. The first-mentioned configuration is used in a particularly important situation of use, namely in relation to freight loading equipment for aircraft, in which freight containers must each be turned through 90.degree. in the region of a load compartment door, during loading and unloading operations.
If, in such a loading operation, a container runs with its flat underside on a caster roller unit, then, if the axes of rotation of its two directly juxtaposed support rollers are not oriented normal to the direction of movement of the container, the caster roller unit will rotate about its vertical axis until the above-described orientation is reached. When that happens, the two support rollers rotate in opposite directions of rotation and roll against the bottom of the container which is disposed thereon, whereby a very small amount of friction is produced After the unit has been turned into the correct orientation, the two support rollers rotate in the same direction, in the direction of movement of the container, and afford same a `weak` guiding action in that direction of movement as they support the container with a linear contact. It will be appreciated that guiding action is not so rigid that the direction of movement of the container could not be altered. If that happens, the caster roller unit rotates about its vertical axis until the axes of rotation of the support rollers are again normal to the new direction of movement of the container.
In the caster roller unit which can be found in U.S. Pat. specification No. 3,435,938, in order to achieve the above-described functions, the roller carrier which is approximately in the form of a downwardly tapering right circular truncated cone is fixed to a base member by means of a vertically arranged bolt which extends along the axis of symmetry of the truncated cone, and a nut which is screwed on to said bolt, in such a way that the roller carrier is rotatable about the fixing bolt, with an annular ball bearing assembly serving as a support means in relation to the base member. Laterally of the fixing bolt the roller carrier has two openings in which the two carrier wheels or rollers are respectively arranged rotatably about a horizontal axis in such a way that their peripheral surfaces project beyond the upward surface of the roller carrier in order to support the article to be moved. In that arrangement the two support rollers are mounted by means of a single shaft which extends through the assembly and which is arranged eccentrically with respect to the vertical bolt and which is fixedly mounted on the roller carrier and on which each of the two support rollers is freely rotatably mounted by means of ball bearing assemblies.
The disadvantages of that known caster roller unit are that it involves a high level of production expenditure and is of comparatively great weight. In particular the roller carrier is of such a complicated form that the production thereof requires a multiplicity of machining steps involving boring, turning and milling operations. In addition assembly of the individual components is not an entirely simple procedure as screwing operations have to be carried out and it is only after the support rollers have been fitted into the openings in the roller carrier that the mounting shaft for the support rollers can be passed through the mounting bores thereof in the roller carrier, and through the support rollers, and secured to the roller carrier.